NetworkManager developers have improved the behavior of wireless network scanning by using wpa_supplicant's WiFi list and by setting the expiry age so no WiFi network seen in 4 minutes will be dropped or if not see nin in the past two scans.
NetworkManager 1.2 was also ported to GDBus for replacing the old dbus-glib library.
More details on the improved WiFi scanning support of NetworkManager 1.2 can be found via this blog post by Red Hat's Dan Williams. Besides this GDBus porting, improved WiFi scanning, and MAC address randomization, a lot of other work has also gone into NM 1.2.
The NetworkManager 1.2 release appears imminent and other changes can also be found via their Git change-log.